SOHC-type valve operating system in internal combustion engine

Abstract: An SOHC-type valve operating system in an internal combustion engine having a single cam shaft commonly provided for a pair of intake valves (16) and a pair of exhaust valves (20). A plurality of intake valve driving members (27₁) are rockably disposed between the cam shaft and the pair of intake valves (16) and have an operative-connection switchover mechanism for switching over the connection and disconnection of the intake valve driving members (27₁). A pair of exhaust valve driving members (27₂) are rockably disposed between the cam shaft and the pair of exhaust valves (20) and independently operate each of the exhaust valves (20). The operative-connection switchover mechanism includes a switchover pin movable between a position for operatively connecting adjacent intake valve driving members (27₁) and a position for releasing such connection, which pin is slidably mounted in a cylindrical sleeve secured to the intake valve driving members for guiding the movement of the switchover pin. The cylindrical sleeve also rotatably supports a cylindrical rotor (45,46,47,48) in rolling contact with a cam (29,30,31,32) provided on the cam shaft. The operative-connection switchover mechanism is disposed on the opposite side of the intake valves (16) with respect to the rocking axis (37) of the intake valve driving member (27₁) whereby space for disposing a component such as an ignition plug (79) is available on the intake side of the engine.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to an SOHC-type valve operating system in an internal combustion engine having a single cam shaft commonly provided for a pair of intake valves and a pair of exhaust valves, a plurality of intake valve driving members rockably disposed between said cam shaft and said pair of intake valves and having an operative-connection switchover mechanism for switching-over between an operative connection and disconnection of the intake valve driving members, and a pair of exhaust valve driving members rockably disposed between said cam shaft and said pair of exhaust valves and respectively corresponding to said exhaust valves, wherein said operative-connection switchover mechanism comprises switchover pin means movable between a position for operatively connecting adjacent intake valve driving members and a position for releasing such connection, and a plug pipe is provided in a cylinder head in which pipe an ignition plug is to be inserted. DESCRIPTION OF THE PRIOR ART Such an SOHC-type valve operating system is known from EP 45 21 58 A1. In this system the plug pipe is provided between said pair of exhaust valves. A similar system is known from Japanese, patent Application Lay-Open Print No. 1405/92. This system includes three valve side rocker arms, two of which are operatively connected at their one ends to a pair of intake valves. Rollers in rolling contact with a cam are rotatably supported on the other ends of the rocker arms, so as to reduce fricitional loss. However, since an operative connection switchover mechanism having a rocker arm is provided between one end of the rocker arms of each intake valve and the rocker arms of the pair of exhaust valves to be operatively connected individually to the pair of exhaust valves are arranged at both sides of the three rocker arms of the side of the intake valves, an ignition plug must be disposed between the rocker arms on the side of both the exhaust valves. However, if the ignition plug is disposed at the exhaust side, it is difficult to improve thermal extraction of the ignition plug. As a result, in order to prevent the occurrence of knocking, the ignition timing cannot be set near an ignition timing for generating a maximum torque, and there arises a problem in which a sufficient torque is not obtained. Further, when the above-described structure is applied to a vehicle-mounted V-type internal combustion engine in which an intake side is disposed inwardly, there also arises a problem in which the space for attaching and detaching the spark plug is inadequate around the internal combustion engine. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an SOHC-type valve operating system in an internal combustion engine which can reduce frictional loss and provide space for disposing a component such as an ignition plug at an intake valve side. In order to achieve the above object, the SOHC-type valve operating system as described in the beginning is characterized in that cylindrical sleeve means is secured to said intake valve driving members for guiding the movement of said switchover pin means, that said cylindrical sleeve means rotatably supports a cylindrical rotor thereon which is in rolling contact with a cam provided on said cam shaft, that said operative-connection switchover mechanism is disposed at an opposite side of said intake valves with respect to a rocking axis of said intake valve driving members, and that said plug pipe is provided between said pair of intake valves. Advantageous designs of the invention are described in the subclaims. The above and other objects, features and advantages of the invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figs.1 to 7 illustrate one embodiment of the present invention, wherein Fig.1 is an end view of a V-type internal combustion engine; Fig.2 is an enlarged sectional view taken along line 2-2 in Fig.1; Fig.3 is a sectional view taken along line 3-3 in Fig.2; Fig.4 is a sectional view taken along line 4-4 in Fig.2; Fig.5 is a sectional view taken along line 5-5 in Fig.3; Fig.6 is a sectional view taken along line 6-6 in Fig.5; Fig.7 is an explanatory view for illustrating the relationship between the operating timing of an intake valve and the operating timing of an operative-connection switchover mechanism; Fig.8 is a sectional view, similar to Fig.5, of a second embodiment of the present invention; Figs.9 and 10 illustrate a first modified embodiment of a sleeve fixing structure, wherein Fig.9 is a sectional view similar to Fig.8, and Fig.10 is a sectional view taken along line 10-10 in Fig.9; Fig.11 is a sectional view, similar to Fig.10, of a second modified embodiment of the sleeve fixing structure; Figs.12 and 13 illustrate a third modified embodiment of the sleeve fixing structure, wherein Fig.12 is a sectional view, similar to Fig.8; and Fig.13 is a sectional view taken along line 13-13 in Fig.12; Fig.14 is a sectional view, similar to Fig.8, of a fourth modified embodiment of the sleeve fixing structure; Fig.15 is a sectional view, similar to Fig.8, of a fifth modified embodiment of the sleeve fixing structure; Fig.16 is a sectional view, similar to Fig.8, of a sixth modified embodiment of the sleeve fixing structure; Fig.17 is a sectional view, similar to Fig.8, of a seventh modified embodiment of the sleeve fixing structure; Fig.18 is a sectional view, similar to Fig.8, of an eighth modified embodiment of the sleeve fixing structure; Fig.19 is a sectional view, similar to Fig.8, of a ninth modified embodiment of the sleeve fixing structure; Fig.20 is a sectional view, similar to Fig.8, of a third embodiment of the invention; Fig.21 is a sectional view, similar to Fig.8, of a fourth embodiment of the invention; Fig.22 is a sectional view, similar to Fig.21, of tenth modified embodiment of the sleeve fixing structure; Fig.23 is a sectional view, similar to Fig.21, of eleventh modified embodiment of the sleeve fixing structure; Figs.24, 25 and 26 illustrate a twelfth modified embodiment of the sleeve fixing structure, wherein Fig.24 is a sectional view similar to Fig.21; Fig.25 is a perspective view of a sleeve fixed to a rocker arm of the side of the third intake valve; Fig.26 is a perspective view of the sleeve fixed to the rocker arm of the side of the second intake valve; Figs.27, 28 and 29 illustrate a thirteenth modified embodiment of the sleeve fixing structure, wherein Fig.27 is a sectional view similar to Fig.21; Fig.28 is a view taken along line 28-28 in Fig.27; and Fig.29 is a front view of a locking member. DESCRIPTION OF THE PREFERRED EMBODIMENTS First, referring to Figs.1 to 7, a first embodiment of the present invention will now be described. Fig.1 is an end view of a V-type internal combustion engine. In this engine, one or a plurality of cylinders 7 arranged in an axial direction of a crankshaft 6, and a second one or a plurality of cylinders 7 arranged in the axial direction of the crankshaft 6 and disposed substantially in a V-shape opened upwardly with respect to the former cylinders 7 are provided in a cylinder block 8. Intake ports 10 of the respective cylinders 7 are provided inside the V-shape and exhaust ports 11 of the respective cylinders 7 are provided outside the V-shape in cylinder heads 9 and 9 connected to the cylinder block 8. And an intake manifold M connected to the respective intake ports 10 is disposed between the cylinder heads 9 and 9. Referring also to Figs.2 to 4, pistons 12 are slidably fitted into the respective cylinders 7. Combustion chambers 13 are defined between upper surfaces of the respective pistons 12 and the cylinder heads 9. A pair of intake valve openings 14 and a pair of exhaust valve openings 15 are provided in the cylinder head 9 so as to open the ceilings of the respective combustion chambers 13. Both the intake valve openings 14 respectively communicate with the intake ports 10, and both the exhaust valve openings 15 respectively communicate with the exhaust ports 11. A pair of intake valves 16 can open and close both the respective intake valve openings 14 separately, and are slidably fitted in guide cylinders 17 provided in the cylinder head 9. Valve springs 19 and 19 are compressed between the cylinder head 9 and retainers 18, 18 provided at the upper ends of the intake valves 16 and 16 protruding upwards from the respective guide cylinders 17 for surrounding the respective intake valves 16 and 16. Therefore, the intake valves 16 and 16 are urged in a direction for closing the intake valve openings 14. A pair of exhaust valves 20 and 20 for opening and closing both the respective exhaust valve openings 15 separately are slidably fitted in guide cylinders 21 provided in the cylinder head 9. Valve springs 23 and 23 are compressed between the cylinder head 9 and retainers 22,22 provided at the upper ends of the exhaust valves 20 and 20 protruding upwards from the respective guide cylinders 21 for surrounding the respective exhaust valves 20 and 20 in a direction for closing the exhaust valve openings 15. Intake valve driving means 27₁ for converting a rotating motion of a cam shaft 26 into opening and closing motions of the intake valves 16, 16 is provided between these valves and the cam shaft 26. The cam shaft 26 is operatively connected to the crankshaft 6 at a reduction ratio of ½. Exhaust valve driving means 27₂ for converting a rotating motion of the cam shaft 26 to opening and closing motions of the exhaust valves 20 and 20 is provided between both the exhaust valves 20, 20 and the cam shaft 26. Referring also to Fig.5, the cam shaft 26 is rotatably supported by the cylinder head 9 and by a holder 28 connected to the cylinder head 9 on an axis parallel to the rotating axis of the crankshaft 6. Fixedly secured to or integrally formed on the cam shaft 26 are: a high speed cam 29 for the intake valves, an intermediate speed cam 30 for the intake valve disposed at one side of the high speed cam 29 so as to correspond to one of the intake valves 16, a low speed cam 31 on the opposite side to the intermediate speed cam 30 with respect to the high speed cam 29, and cams 32 and 32 for the exhaust valves 20 and 20 separately corresponding there to at opposite sides of the intermediate speed cam 30 and the low speed cam 31. The high speed cam 29 for the intake valve has a shape suitable for opening and closing both the intake valves 16 and 16 in a high speed operating region of the internal combustion engine. The cam 29 includes an arc-shaped base circle portion 29a around the axis of the cam shaft 26, and a lobe 29b extended radially outward from the base circle portion 29a. The intermediate speed cam 30 for the intake valves 16 has a shape suitable for opening and closing one of the intake valves 16 in a low speed operating region of the internal combustion engine. The cam 30 includes an arc-shaped base circle portion 30a around the cam shaft 26, and a lobe 30b extended from the base circle portion 30a. The lobe 30b is extended from the base circle portion 30a a less amount and at a narrower angle than the lobe 29b. The low speed cam 31 for the intake valve 16 has a shape suitable for opening and closing the other intake valve 16 in a low speed operating region of the engine. The cam 31 includes an arc-shaped base circle portion 31a around the axis of the cam shaft 26, and a lobe 31b extended from the base circle portion 31a. The lobe 31b is extended from the base circle portion 30a a less amount and at a narrower angle than the lobe 30b. Further, the width W₂ of the intermediate speed cam 30 for the intake valve is shorter along the axial direction thereof than the width W₁ of the high speed cam 29 for the intake valves. The width W₃ of the low speed cam 31 for the intake valve along is shorter along the axial direction thereof than the width W₂ of the intermediate speed cam 30. Further, cams 32 and 32 for the exhaust valves have a shape suitable for opening and closing both the exhaust valves 20 in the same manner irrespective of the operating state of the engine. The intake valve driving means 27₁ includes first, second and third intake valve side rocker arms 33₁, 34₁, 35₁ as intake valve driving members disposed adjacent to each other; and an operative-connection switchover mechanism 36₁ for switching over the connection and disconnection of the rocker arms 33₁ to 35₁. The first intake valve side rocker arm 33₁ is operatively connected to the one intake valve 16, the third intake valve side rocker arm 35₁ is operatively connected to the other intake valve 16, and the second intake valve side rocker arm 34₁ is disposed between the first and third intake valve side rocker arms 33₁ and 35₁. The first to third intake valve side rocker arms 33₁ to 35₁ are rockably supported by an intake valve side rocker arm shaft 37 which is secured to the holder 28 at an obliquely upper position relative to the cam shaft 26. The exhaust valve driving means 27₂ includes a pair of exhaust valve side rocker arms 38₁ and 38₁ as exhaust valve driving members to be operatively connected independently to the respective exhaust valves 20 and 20. The exhaust valve side rocker arms 38₁ are rockably supported by an exhaust valve side rocker arm shaft 39 secured to the holder 28 at an obliquely upper position relative to the cam shaft 26. The first to third intake valve side rocker arms 33₁ to 35₁ are adjacently disposed between the holders 28 that disposed on opposite sides of the cylinders 7 along the axis of the crankshaft 6. Both the exhaust valve side rocker arms 38₁ are disposed between the holders 28 and biased away from each other by a coil spring 42 surrounding the exhaust valve side rocker arm shaft 39. In the intake valve driving means 27₁, arms 33a and 35a extended toward the intake valves 16 are integrally provided with the first and third intake valve side rocker arms 33₁ and 35₁. Tappet screws 40 to be abutted against the upper ends of both the intake valves 16 are threadedly fitted into the tip ends of the arms 33a and 35a for advancing and retreating movements. In the exhaust valve driving means 27₂, arms 38a extended toward the exhaust valves 20 are integrally provided with the exhaust valve side rocker arms 38₁, and tappet screws 41 to be abutted against the upper ends of both the exhaust valves 20 are threadedly fitted into the tip ends of the arms 38a for advancing and retreating movements. In the first intake valve side rocker arm 33₁, a cylindrical rotor 45 in rolling contact with the intermediate speed cam 30 for the intake valve is rotatably supported on the opposite side end to the intake valve 16 with respect to the rocking axis of the rocker arm 33₁, i.e., the axis of the intake valve side rocker arm shaft 37. In the second intake valve side rocker arms 34₁, a cylindrical rotor 46 in rolling contact with the high speed cam 29 for the intake valves is rotatably supported on the opposite side end to the intake valves 16 with respect to the rocking axis of the rocker arm 34₁. In the third intake valve side rocker arm 35₁, a cylindrical rotor 47 in rolling contact with the low speed cam 31 for the intake valve is rotatably supported on the opposite side end to the intake valve 16 with respect to the rocking axis of the rocker arm 35₁. In the exhaust valve side rocker arms 38₁, cylindrical rotors 48 in rolling contact with the cams 32 for the exhaust valves 20 are rotatably supported on the opposite ends to the exhaust valves 20 and 30 with respect to the rocking axis of the rocker arm 38₁, i.e., the axis of the exhaust valve side rocker arm shaft 39. In the first intake valve side rocker arm 33₁, a bottomed fitting hole 49 opened toward the second intake valve side rocker arm 34₁ is provided in parallel with the intake valve side rocker arm shaft 37. The second intake valve side rocker arm 34₁ is provided with a fitting hole 50 opened to both side surfaces of the rocker arm 34₁ so as to correspond to the fitting hole 49. The third intake valve side rocker arm 35₁ is provided with a bottomed fitting hole 51 opened toward the second intake valve side rocker arm 34₁ in parallel with the intake valve side rocker arm shaft 37 so as to correspond to the fitting hole 50. Cylindrical sleeves 52₁, 53₁, 54₁of the same diameters are fitted and fixed in the fitting holes 49, 50 and 51, for example, by press-fitting. A plurality of rollers 55, 56, 57 are respectively interposed between the sleeves 52₁ to 54₁ and the rotors 45 to 47 which coaxially surround these sleeves. The exhaust valve side rocker arms 38₁ are provided with fitting holes 58 opened at both the side faces in parallel with the exhaust valve side rocker arm shaft 39. A plurality of rollers 60 are respectively interposed between the cylindrical sleeves 59₁ fitted and fixed in the fitting holes 58, for example, by press-fitting and the rotors 48 for coaxially surrounding the sleeves 59₁. Therefore, the first to third intake valve side rocker arm 33₁ to 35₁ are respectively driven by the corresponding cams 30, 29 and 31 through the rotors 45 to 47. In addition, since the relationship of (the width W₁ of the high speed cam 29) > (the width W₂ of the intermediate cam 30) > (the width W₃ of the low speed cam 31) is established, the axis lengths of the rotors 46, 45 and 47 are so set as to satisfy the relationship of (the axial length of the rotor 46) > (the axial length of the rotor 45) > (the axial length of the rotor 47). Further, the exhaust valve side rocker arms 38₁ are respectively driven by the cams 32 for the exhaust valves 20 through the rotors 48. A supporting plate 61 is secured onto the holders 28 above the intake valve side rocker arms 33₁ to 35₁ and the exhaust valve side rocker arms 38₁. On the supporting plate 61, a lost motion mechanism 62 for resiliently urging the second intake valve side rocker arm 34₁ in a direction so that the rotor 46 is contacted with the high speed cam 29 for the intake valves. The lost motion mechanism 62 includes a guide member 63 which is secured to the supporting plate 61 and formed into a bottomed cylindrical shape opened downwards, a lifter 64 which is slidably fitted to the guide member 63 and abutted at its tip end against the second intake valve side rocker arm 34₁, and a lifter spring 65 compressed between the lifter 64 and the guide member 63. The operative-connection switchover mechanism 36₁ includes a first switchover pin 68 for switching over the connection and disconnection of the third and second intake valve side rocker arms 35₁ and 34₁, a second switchover pin 69 capable of switching over the connection and disconnection of the second and first intake valve side rocker arms 34₁ and 33₁, a restrain member 70 slidably contacted with the second switchover pin 69 at the opposite side from the first switchover pin 68, and a return spring 71 for urging the restrain member 70 toward the second switchover pin 69. The first switchover pin 68 includes a spring compressed between a bottomed cylindrical urging member 81 and a short columnar locking member 82. The pin 68 is slidably fitted in the sleeve 54₁ of the third intake valve side rocker arm 35₁. Further, a fluid pressure chamber 72 is defined between the closed end of the fitting hole 51 of the third intake valve side rocker arm 35₁ and the urging member 81 of the first switchover pin 68. A communication passage 73 communicating with the fluid pressure chamber 72 is provided in the third intake valve side rocker arm 35₁. A fluid pressure passage 74 always communicating with the communication passage 73 is provided in the intake valve side rocker arm shaft 37. The fluid pressure passage 74 is connected to a fluid pressure source through a control valve (not shown). The second switchover pin 69 is slidably fitted in the sleeve 53₁ of the second intake valve side rocker arm 34₁. One end of the second switchover pin 69 is slidably contacted with an end face of the locking member 82 of the first switchover pin 68. The restrain member 70 is slidably fitted in the sleeve 52₁ of the first intake valve side rocker arm 33₁. A closed end of the restrain member 70 is slidably contacted with the other end of the second switching pin 69. A snap ring 75 for abutting against the restraining member 70 and preventing the latter from dropping out of the sleeve 52₁ is attached to the inner surface of the sleeve 52₁. The return spring 71 is compressed between the restraining member 70 and the closed end of the fitting hole 49 of the first intake valve side rocker arm 33₁. An opening hole 76 is provided in the closed end of the fitting hole 49. In the first switchover pin 68, an engaging step portion 84 is provided on an outer periphery of the edge of the urging member 81 near the locking member 82, and an annular engaging groove 85 is provided on the outer surface of the intermediate portion of the urging member 81. Further, a timing plate 88 of a triggering mechanism 87 can be engaged with the engaging step portion 84 and the engaging groove 85. A groove 86 for slidably engaging the engaging portion 88a of the timing plate 88 is provided on the lower portion of the third intake valve side rocker arm 35₁. The groove 86 is located at a position corresponding the engaging step portion 84 in a state that the urging member 81 is moved to the maximum limit toward the fluid pressure chamber 72. The position of the engaging groove 85 is defined such that it becomes a position corresponding to the groove 86 when a fluid pressure is applied to the fluid pressure chamber 72 so that the urging member 81 is moved to the maximum limit in a direction for pressing the locking member 82 thereby to completely connect the third and second intake valve side rocker arms 35₁ and 34₁ through the locking member 82. Referring also to Fig.6, the triggering mechanism 87 includes: a timing plate 88 which has an engaging portion 88a to be fitted in the groove 86 and which is supported on the intake valve side rocker arm shaft 37 for rocking with the third intake valve side rocker arm 35₁; a torsion spring 89 engaged, at its one end, with the timing plate 88 and surrounding the intake valve side rocker arm shaft 37; and a pin 90 capable of engaging with a stopper 88b protruding from the timing plate 88 and engaged with the other end of the torsion spring 89. The pin 90 is embedded in the holder 28. In such a triggering mechanism 87, the engaging portion 88a of the timing plate 88 is engaged with the engaging step portion 84 or the engaging groove 85 from the groove 86 in a state where the third intake valve side rocker arm 35₁ is slidably contacted with the base circle portion 31a of the low speed cam 31 for the intake valve and stopped, and is disengaged from the groove 86 when the third intake valve side rocker arm 35₁ is slidably contacted with the lobe 31b of the low speed cam 31 for the intake valve for rockably moving the intake valve 16 in a direction for opening the intake valve 16. An ignition plug 78 is arranged at the center of the ceiling of the combustion chamber 13. A plug pipe 79 in which the ignition plug 78 is to be inserted is provided in the cylinder head 9. In the intake valve driving means 27₁, the intake valve side rocker arms 33₁ to 35₁ are respectively driven by the cams 30, 29, 31 of the cam shaft 26 through the rotors 45 to 47 at the opposite side from the intake valves 16 with respect to the intake valve side rocker arm shaft 37. Since the operative-connection switchover mechanism 36₁ is coaxially disposed with the rotors 45 to 47, a vacant space is provided between the arms 33a and 35a of the first and third intake valve side rocker arms 33₁ and 35₁ and thus, the plug pipe 79 can be mounted in the vacant space. Therefore, in a V-type internal combustion engine for a vehicle in which the intake side is disposed inside the V, the plug pipe 79 for attaching and detaching the ignition plug 78 can be arranged inside the V of the V-type internal combustion engine. The operation of the first embodiment described above will now be described. In the low speed operating region of the internal combustion engine, the fluid pressure is not applied to the fluid pressure chamber 72 of the operative-connection switchover mechanism 36₁. The slidably contacting surfaces of the first and second switchover pins 68 and 69 are located at corresponding positions between the third and second intake valve side rocker arms 34₁ and 35₁. The slidably contacting surfaces of the second switchover pin 69 and the restrain member 70 are located at corresponding positions between the second and first intake valve side rocker arms 34₁ and 33₁. Therefore, the intake valve side rocker arms 33₁ to 35₁ are capable of rocking relative to each other. Thus, one of the intake valves 16 is driven for opening and closing at the timing and the lift amount in accordance with the intermediate speed cam 30 for that intake valve, while the other intake valve 16 is driven for opening and closing at the timing and the lift amount in accordance with the low speed cam 31 for that intake valve. In this state, the first switchover pin 68 is in a state where it is displaced to the maximum limit toward the fluid pressure chamber 72. The engaging portion 88a of the timing plate 88 of the triggering mechanism 87 is engaged with the engaging step portion 84 when the third intake valve side rocker arm 35₁ is in a stopped state, and is disengaged from the engaging step portion 84 in response to the rocking operation of the third intake valve side rocker arm 35₁ in a direction for opening the intake valve 16. As shown in Fig.7, in the high speed operating region of the internal combustion engine, when the fluid pressure is applied to the fluid pressure chamber 72 at a timing t₁ of a valve closing zone Vc of the intake valves 16, the urging member 81 of the first switchover pin 68 tries to start moving. But since the engaging portion 88a of the timing plate 88 is engaged with the engaging step portion 84, the movement of the urging member 81 is prevented, and the first switchover pin 68 is kept in a state as shown in Fig.5. Then, when the engine enters a valve opening zone Vo of the intake valves 16 and the third intake valve side rocker arm 35₁ starts rocking, the third intake valve side rocker arm 35₁ leaves the timing plate 88 and the engaging portion 88a of the timing plate 88 is disengaged from the engaging step portion 84. In this manner, the urging member 81 tries to start moving, but engagement of the locking member 82 with the sleeve 53₁ is prevented by the displacement of the axis of the sleeve 54₁ of the third intake valve side rocker arm 35₁ from the axis of the sleeve 53₁ of the second intake valve side rocker arm 34₁ due to the rocking of the third intake valve side rocker arm 35₁. When next valve closing zone Vc is started, the axes of the sleeves 53₁ and 54₁are brought substantially into coincidence so that the urging member 81 urges the locking member 82 which starts moving. Thus, the locking member 82 is fitted into the sleeve 53₁, the second switchover pin 59 is fitted into the sleeve 52₁, and the first to third intake valve side rocker arms 33₁ to 35₁ are integrally connected. In this manner, both the intake valves 16 are driven to be opened and closed at the timing and the lift amount in accordance with the high speed cam 29 of the intake valves. When the operative-connection switchover mechanism 36₁ is in an operatively connecting state, the engaging groove 85 is located at a position corresponding to the groove 86, and the engaging portion 88a of the timing plate 88 is engaged with the engaging groove 85 in the valve closing zone Vc. Then, when the fluid pressure is released from the fluid pressure chamber 72 at the timing t₁ of the valve closing zone Vc, of the first switchover pin 68 is pressed by the return spring 71 toward the fluid pressure chamber 72. But since the engaging portion 88a is engaged with the engaging groove 85, the movement of the first switchover pin 68 is prevented. When the engine enters the valve opening zone Vo, the engaging portion 88a of the timing plate 88 is disengaged from the engaging groove 85 in response to the rocking operation of the third intake valve side rocker arm 35₁, and the urging member 81 is moved by a force of the spring 83 toward the fluid pressure chamber 72. In this case, the locking member 82 is not returned toward the sleeve 54₁ because of the frictional force with the inner surfaces of the sleeves 53₁ and 54₁, but is moved toward the sleeve 54₁ and returned to the state shown in Fig.5 when the engine enters the next valve closing zone Vc. When the fluid pressure is applied to the fluid pressure chamber 72 at the timing t₂ of the valve opening zone Vo during transfer from the low speed operating region to the high speed operating region, the engaging portion 88a of the timing plate 88 is disengaged from the engaging step portion 84, but the engagement of the locking member 82 with the sleeve 53₁ is prevented because the axis of the sleeve 54₁ of the third intake valve side rocker arm 35₁ and the axis of the sleeve 53₁ of the second intake valve side rocker arm 34₁ are offset from each other. When next valve closing zone Vc is started, the axis of the sleeves 53₁ and 54₁ are brought substantially into coincidence so that the urging member 81 thereby causes the locking member 82 to start moving. Thus, the locking member 82 is engaged with the sleeve 53₁ the second switchover pin 69 is engaged with the sleeve 52₁, and the first to third intake valve side rocker arms 33₁ to 35₁ are integrally connected. In this manner, it is possible to improve the output of the internal combustion engine by the valve operating characteristics being adapted for the operating state of the engine, by varying the opening and closing characteristics of both the intake valves 16 in the low and high speed operating regions of the engine. On the other hand, both the exhaust valves 20 are driven for opening and closing at the same timing and the lift amount in accordance with the cams 32 and 32 for the exhaust valves in both the low and high speed operating regions of the engine. In such a valve operating system, in both the intake valve driving means 27₁ and the exhaust valve driving means 27₂, the rocker arms 33₁ to 35₁, 38₁, 38₁ are respectively driven by the corresponding cams 30, 29, 31, 32, 32 through the rotors 45 to 47, 48, 48. Therefore, the frictional loss is reduced thereby to reduce the required valve opening power. Further, the operative-connection switchover mechanism 36₁ provided at the first to third intake valve side rocker arms 33₁ to 35₁ is coaxially disposed at the rotors 45 to 47. The first switchover pin 68, the second switchover pin 69, the restrain member 70 and the return spring 71 of the operative-connection switchover mechanism 36₁ are inserted into the sleeves 52₁ to 54₁ that are secured to the rocker arms 33₁ to 35₁ to support to the rotors 45 to 47. Therefore, it is not necessary to provide separate holes for constructing the operative-connection switchover mechanism 36₁ at the respective rocker arms 33₁ to 35₁, which contributes to a reduction of the number of the manufacturing steps. Further, since the ignition plugs 78 can be disposed at the side of the intake valves 16, thermal extraction around the ignition plug 78 can be improved. Even if the ignition timing of the ignition plug 78 is set in the vicinity of the preferred ignition timing for generating a maximum torque, occurrence of knocking can be suppressed, and accordingly sufficient output torque of the engine can be obtained. In addition, in the V-type internal combustion engine for the vehicle in which the intake side is disposed inside the V, the ignition plugs 78 are disposed at the side of the intake valves 16. Thus, the space for attaching and detaching the ignition plugs 78 is provided in the upper portion of the V-type internal combustion engine, and it is easy to provide the space for attaching and detaching the ignition plugs 78. It is considered in the operative-connection switchover mechanism 36₁ that, even if a high fluid pressure is applied to the fluid pressure chamber 72 and the operative connection of the first and second switchover pins 68 and 69 is disturbed due to some reason whereby the operative-connection switchover mechanism 36₁ remains in a disconnected state the intake valve operation is satisfactory. In this case, the first intake valve side rocker arm 33₁ for driving the intake valve 16 which is actuated at relatively high lift of both the intake valves 16 to be operated independently from one another, in order to provide the valve operating behavior up to a predetermined high speed range, normally it is necessary to set the spring load of the valve spring 19 to a relatively high value corresponding to the weight of the first intake valve side rocker arm 33₁. Therefore, if the first intake valve side rocker arm 33₁ is relatively heavy, the spring load of the valve spring 19 must be correspondingly set to a large value, and the valve opening power required is increased in both the connection and disconnection states. However, since the third intake valve side rocker arm 35₁ is provided with the fluid pressure chamber 72 and the communication passage 73 for driving one of the intake valves 16 which has a lower lift amount, the first intake valve side rocker arm 33₁ can be reduced in weight because the rocker arm 33₁ does not have such chamber 72 and the passage 73. Therefore, the spring load for urging the first intake valve side rocker arm 33₁ can be set to a relatively low value to contribute to a reduction in the required valve opening power. The first switchover pin 68 of the operative-connection switchover mechanism 36₁ is formed to be relatively long so as to engage the engaging portion 88a of the timing plate 88. The relatively short restrain member 70 and return spring 71 may simply be provided in the first intake valve side rocker arm 33₁ by providing the first switchover pin 68 in the third intake valve side rocker arm 35₁ for driving the one of the intake valves 16 having a lower lift amount among the two intake valves 16 independently operated from one another in the disconnected state of the operative-connection switchover mechanism 36₁, which reduces the weight for setting the spring load thereby to reduce the required valve opening power. The third intake valve side rocker arm 35₁ needs, in addition to a portion necessary to slidably contact with the low speed cam 31 for the intake valve 16, a portion necessary to engage the timing plate 88 with the first switchover pin 68 and a portion necessary to provide the fluid pressure chamber 72 and the communication passage 73. However, since the relationship of (the axial length of the rotor 46) > (the axial length of the rotor 45) > (the axial length of the rotor 47) is satisfied, it is possible to set the width of the third intake valve side rocker arm 35₁ along the axis of the intake valve side rocker arm shaft 37 to a relatively small value irrespective of the arrangements of the fluid pressure chamber 72 and the communication passage 73 as well as the arrangement of the first switchover pin 68. Thus, an increase in the weight of the third intake valve side rocker arm 35₁ is suppressed to contribute to a reduction in the required valve opening power as much as possible and the valve operating system may be constructed relatively simply along the axis of the cam shaft 26. The intake valve driving means 27₁ of the first embodiment described above includes the triggering mechanism 87 for determining the operation starting timing of the operative-connection switchover mechanism 36₁. But the present invention can also be applied to intake valve driving means having no triggering mechanism as will be described in a second embodiment shown in Fig.8. The present invention is not limited to the embodiment described above. As a second embodiment shown in Fig.8, the present invention may also be applied to intake valve driving means having no triggering mechanism. The components of this second embodiment and other embodiments that are the same as the first embodiment will be numbered the same and not described in detail again. In Fig.8, an operative-connection switchover mechanism 36₂ includes a first switchover pin 68' for switching over the connection and disconnection of third and-second intake valve side rocker arms 35₁ and 34₁, a second switchover pin 69' for switching over the connection and disconnection of second and first intake valve side rocker arms 34₁ and 33₁, a restrain member 70 slidably contacted with the second switchover pin 69 at the opposite side from the first switchover pin 68', and a return spring 71 for urging the restrain member 70 toward the second switchover pin 69'. The first switchover pin 68' is formed in a short columnar shape and slidably mounted in a sleeve 54₁'. A fluid pressure chamber 72 is defined between a closed end of a fitting hole 51 of the third intake valve side rocker arm 35₁ and the first switchover pin 68'. The second switchover pin 69' is formed in a short columnar shape and slidably mounted in the sleeve 53₁ of the second intake valve side rocker arm 34₁. In order to reliably secure the sleeves to the respective rocker arms 33₁ to 35₁, 38₁, 38₁, it may be possible to use a weld, a caulk or any other convenient means. However, it is preferable to use a heat treatment on a surface of the sleeve for rotatably supporting the cylindrical rotor for obtaining a hardness near H R C 60 taking into account the pitching resistance. It is also preferable to use case-hardening steel and heat treating for the respective rocker arms 33₁ to 35₁, 38₁, 38₁. However, if the heat-treated member is welded, delayed fracture might occur due to residual tensile stress. Further, since a member having high hardness cannot be caulked (meaning squashing or crushing one or both adjoining metal parts to secure them together without heat or any separate joining material), it is difficult to accomplish a fixing structure by welding or caulking in an "as is" condition. In addition, it must be avoided to produce a portion protruding toward adjacent rocker arm side by fixing the sleeves to the respective rocker arms 33₁ to 35₁, 38₁, 38₁ in order to simplify the valve operating system. Therefore, a modified embodiment in which a sleeve is reliably fixed to a rocker arm in a simple fixing structure will now be described. Figs.9 and 10 illustrate a first modified example of a sleeve fixing structure, and the similar reference numerals are given to components corresponding to those of the previous embodiment. Engaging holes 91, 92, 93 are respectively provided in the first, second and third intake valve side rocker arms 33₁, 34₁, 35₁. Sleeves 52₂, 53₂, 54₂ are welded and secured to the respective rocker arms, 33₁, 34₁, 35₁ in a state where the sleeves 52₂, 53₂, 54₂ are respectively engaged in the fitting holes 91, 92, 93. Connection switching means 36₂ includes a first switchover pin 68', a second switchover pin 69', a restrain member 70, and a return spring 71. The first switchover pin 68' can be slidably mounted within the sleeve 54₂ so that the pin 68' is slidably engageable with the sleeve 53₂. A fluid pressure chamber 72 is defined between one end of the first switchover pin 68' and a bottomed cylindrical lid member 94 for closing one end of the sleeve 54₂. The second switchover pin 69' can be slidably mounted within the sleeve 53₂ and slidably engageable with the sleeve 52₂. The restrain member 70 is slidably mounted within the sleeve 52₂. The opposite side end of the sleeve 52₂ to the second intake valve side rocker arm 34₁ is closed by a lid member 95 coaxially having an opening hole 96. The return spring 71 is compressed between the lid member 95 and the restrain member 70. The first, second and third intake valve side rocker arms 33₁, 34₁, 35₁ are formed of case-hardening steel whose surface is subjected to a quenching treatment. The fitting holes 91, 92, 93 are respectively provided in the rockers 33₁, 34₁, 35₁ so that case-hardening layers do not remain on inner surfaces at the time of finishing. On the other hand, the sleeves 52₂, 53₂, 54₂ are quenched so that the surface hardness becomes about H R C 60. If the first, second and third intake valve side rocker arms 33₁, 34₁, 35₁ are welded to the sleeves 52₂, 53₂, 54₂ so as to reliably fix these sleeves to the rocker arms in a state where the quenched portions remain, a delayed fracture might occur due to residual tensile stress. Therefore, the intake valve side rocker arms 33₁, 34₁, 35₁ are subjected to a counter boring treatment so as to form recesses 91a, 92a, 93a to be recessed axially inward on both ends of the fitting holes 91, 92, 93 thereby to remove the quenched portions of both ends of the fitting holes 91, 92, 93. Then, both ends of the sleeves 52₂, 53₂, 54₂ are cut off and removed thereby to remove the quenched portions, and the rocker arms are respectively welded to the sleeves in the recesses 91a, 92a, 93a over the entire peripheral surfaces as shown in Fig.10. In this case, a large-diameter portion 94a to be engaged with one end of the sleeve 54₂ is provided integrally with the lid member 94 for closing the one end Of the sleeve 54₂ and the large-diameter portion 94a is welded together with the sleeve 54₂ to the third intake valve side rocker arm 35₁. A large-diameter portion 95a to be engaged with the end of the sleeve 52₂ is provided integrally with the lid member 95 for closing the end of the sleeve 52₂, and the large-diameter portion 95a is welded together with the sleeve 52₂ to the third intake valve side rocker arm 33₁. The sleeves 59₂, 59₂ are fixed to the exhaust valve side rocker arms 38₁, 38₁ in a structure similar to the welding fixing structure of the second intake valve side rocker arm 34₁ to the sleeve 53₂. According to the first modified embodiment described above, a delayed fracture due to residual tensile stress is prevented, and the sleeves 52₂, 53₂, 54₂, 59₂, 59₂ can be reliably fixed to the respective rocker arms 33₁, 34₁, 35₁, 38₁, 38₁. The lid members 94 and 95 are welded together with the sleeves 54₂, 52₂ to the respective third and first intake valve side rocker arms 35₁ and 33₁ thereby to simplify assembling steps and efficiently assemble them. Further since the intake valve side rocker arms 33₁, 34₁, 35₁ are welded to the respective sleeves 52₂, 53₂, 54₂ in the recesses 91a, 92a, 93a, the welded portions do not protrude toward the adjacent rocker arms, but the rocker arms 33₁ to 35₁ can be simply disposed. Fig.11 illustrates a second modified embodiment of the sleeve fixing structure. Rocker arms 33₁, 34₁, 35₁, 38₁, 38₁ may be welded to the respective sleeves 52₂, 53₂, 54₂, 59₂, 59₂ at a plurality of positions in a circumferential direction. Figs.12 and 13 illustrate a third modified embodiment of the sleeve fixing structure. Sleeves 52₃, 53₃, 54₃ are respectively fixed to intake valve side rocker arms 33₁, 34₁, 35₁, and the outer ends of the sleeves 54₃, 52₃ are closed by press-fitting lid members 97 and 98. Sleeves 59₃ are fixed to both exhaust valve side rocker arms 38₁. In order to secure the sleeves 52₃, 53₃, 54₃ to the respective intake valve side rocker arms 33₁, 34₁, 35₁, quenched portions of both ends of fitting holes 91, 92, 93 are removed by the counter boring treatment. Stepped connecting portions 101, 102, 103 directed axially outward are respectively formed at both axial ends of the sleeves 52₃, 53₃, 54₃, and circular recesses 104, 105, 106 recessed axially inward are respectively formed at both ends of the fitting holes 91, 92, 93 and both ends of the sleeves 52₃, 53₃, 54₃. In order to form the connecting portions 101, 102, 103, the quenched portions of both ends of the sleeves 52₃, 53₃, 54₃ may remain as they are. That is, the sleeves 52₃, 53₃, 54₃ may be quenched in the state having the connecting portions 101, 102, 103. The intake valve side rocker arms 33₁, 34₁, 35₁ are caulked, such as by crushing one of the components in an axial direction with a circular die, so as to connect the inner faces of the ends of the fitting holes 91, 92, 93 in which the quenched portions are removed to the corresponding connecting portions 101, 102, 103 over the entire peripheral surfaces in recesses 104, 105, 106 thereby to secure the sleeves 52₃, 53₃, 54₃ to the intake valve side rocker arms 33₁, 34₁, 35₁. Sleeves 59₃, 59₃ are secured to both the exhaust valve side rocker arms 38₁, 38₁ in the same manner as the caulked fixing structures of the sleeves 52₃ to 54₃ to the intake valve side rocker arms 33₁ to 35₁. The sleeves 52₃, 53₃, 54₃, 59₃, 59₃ can reliably be secured to the corresponding rocker arms 33₁ to 35₁, 38₁, 38₁ even by the third modified embodiment as described above. Fig.14 illustrates a fourth modified embodiment of the sleeve fixing structure. Rocker arms 33₁, 34₁, 35₁, 38₁, 38₁ may be caulked at a plurality of positions in a circumferential direction and connected to sleeves 52₃ to 54₃, 59₃, 59₃. Fig.15 illustrates a fifth modified embodiment of the sleeve fixing structure. In securing the sleeves 52₄, 53₄, 54₄ to first to third intake valve side rocker arms 33₁ to 35₁, quenched portions of both axial ends of the sleeves 52₄, 53₄, 54₄ are removed by the counter boring treatment. Stepped connecting portions 107, 108, 109 directed axially outward are formed at both ends of fitting holes 91, 92, 93 and both ends of the sleeves 52₄, 53₄, 54₄. In order to form the connecting portions 107, 108, 109, quenched portions of both ends of the rocker arms 33₁, 34₁, 35₁ may be quenched in the state having the connecting portions 107, 108, 109. In this state, outer faces of the ends of the sleeves 52₄, 53₄, 54₄ in which inner peripheral edges of the recesses 110, 111, 112, i.e., quenched portions are removed, are caulked to be connected in these recesses over the entire peripheral surfaces of the corresponding connecting portion 107, 108, 109 thereby to secure the sleeves 52₄, 53₄, 54₄ to the respective intake valve side rocker arms 33₁ to 35₁. Sleeves 59₄, 59₄ are secured to both exhaust valve side rocker arms 38₁ and 38₁ in the same manner. Fig.16 illustrates a sixth modified embodiment of the sleeve fixing structure. Sleeves 52₅ and 54₅ are secured to first and third intake valve side rocker arms 33₁ and 35₁, and a sleeve 53₅ is secured to a second intake valve side rocker arm 34₁ similar to the third modified embodiment of Figs.12 and 13. The sleeves 59₅ and 59₅ are secured to both exhaust valve side rocker arms 38₁, 38₁ similar to the third modified embodiment of Figs.12 and 13. In order to secure the sleeves 52₅ and 54₅ to the first and third intake valve side rocker arms 33₁ and 35₁, quenched portions of both ends of fitting holes 91 and 93 are removed by the counter boring treatment so that stepped portions 113 and 114 directed axially outward are formed at one end of each of the fitting holes 91 and 93. Connecting portions 115 and 116 extended radially outward for being supported on the stepped portions 113 and 114 are provided at axial one end of each of the sleeves 52₅ and 54₅ and stepped connecting portions 52₅ and 54₅ directed axially outward are formed at the other axial end of each of the sleeves 52₅ and 54₅. Thus, circular recesses 117 and 118 recessed axially inward are formed on one end of each of the fitting holes 91, 93 and one end of each of the sleeves 52₅ and 54₅, and circular recesses 104 and 106 recessed axially inward are formed on the other end of each of the fitting holes 91 and 93 and the other end of each of the sleeves 52₅ and 54₅. Further, the quenched portions of the connecting portions 115, 116 of the axial one end and the connecting portions 101, 103 of the axial other end of each of the sleeves 52₅ and 54₅ may remain. The rocker arms 33₁ and 35₁ are caulked at one end of each of the fitting holes 91 and 93 such that the arms can be connected to the connecting portions 115 and 116 to be supported by the stepped portions 113 and 114. The rocker arms 33₁ and 35₁ are caulked at the other end of the fitting holes 91 and 93 such that the outer peripheral edges of the recesses 104 and 106 are connected to the connecting portions 101 and 103. Therefore, the sleeves 52₅ and 54₅ are secured to the respective rocker arms 33₁ and 35₁. According to the sixth modified embodiment, the connecting portions 115 and 116 are supported by the stepped portions 113 and 114 thereby to consistently determine the axial positions of the sleeves 52₅ and 54₅. Fig.17 illustrates a seventh modified embodiment of the sleeve fixing structure. Stepped cylindrical sleeves 52₆, 53₆, 54₆ are fixedly press-fitted into first to third intake valve side rocker arms 33₁, 34₁, 35₁. The sleeve 52₆ is provided at one end thereof with a large-diameter press-fitting portion 121, and a small-diameter support portion 122 coaxially connected to the large-diameter press-fitted portion 121 through a stepped portion 123. The sleeve 52₆ is formed into a stepped bottomed cylindrical shape closed at the other end thereof. The first intake valve side rocker arm 33₁ is provided with, sequentially from the side of the second intake valve side rocker arm 34₁, a large-diameter press-fitted hole 124 in which the large-diameter press-fitted portion 121 is press-fitted, and a small-diameter fitting hole 125 in which the support portion 122 is lightly press-fitted. Both the holes 124 and 125 are coaxially provided through a stepped portion 126 which can abut against the stepped portion 123. The sleeve 52₆ is secured to the first intake valve side rocker arm 33₁ by press-fitting the large-diameter press-fitted portion 121 into the press-fitting hole 124 and by lightly press-fitting the supporting portion 122 into the fitting hole 125. And a rotor 45 is supported on the supporting portion 122 of the sleeve 52₆ through a plurality of rollers 55. The sleeve 53₆ is provided at one end with a large-diameter press-fitted portion 127, a small-diameter supporting portion 128 is coaxially connected to the large-diameter press-fitted portion 127 through a stepped portion 129, and the sleeve 53₆ thereby is formed into a stepped cylindrical shape opened at both ends. The second intake valve side rocker arm 34₁ is provided with, sequentially from the side of the third intake valve side rocker arm 35₁, a press-fitting hole 130 in which the large-diameter press-fitted portion 127 is press-fitted, and a small-diameter fitting hole 131 in which the supporting portion 128 is lightly press-fitted, in a coaxial manner, through a stepped portion 132 which can abut against the stepped portion 129. The sleeve 53₆ is secured to the second intake valve side rocker arm 34₁ by press-fitting the large-diameter press-fitted portion 127 in the press-fitting hole 130 and by lightly press-fitting the supporting portion 128 in the fitting hole 131, and a rotor 46 is supported on the supporting portion 128 of the sleeve 53₆ through a plurality of rollers 56. The sleeve 54₆ is provided at one end with a large-diameter portion 133, a small-diameter supporting portion 134 is coaxially connected to the large-diameter press-fitted portion 133 through a stepped portion 135, and the sleeve 54₆ thereby is formed into a stepped bottomed cylindrical portion shape closed at the other end. The third intake valve side rocker arm 35₁ is provided with, sequentially from the side of the second intake valve side rocker arm 34₁, a press-fitting hole 136 in which the large-diameter press-fitted portion 133 is press-fitted and a small-diameter fitting hole 137 in which the supporting portion 134 is lightly press-fitted, in a coaxial manner, through a stepped portion 138 which can abut against the stepped portion 135. The sleeve 54₆ is secured to the third intake valve side rocker arm 35₁ by press-fitting the large-diameter press-fitted portion 133 in the press-fitting hole 136 and by lightly press-fitting the supporting portion 134 in the fitting hole 137, and a rotor 47 is supported on the supporting portion 134 of the sleeve 54₆ through a plurality of rollers 57. Further, the sleeves 59₆ are secured to both exhaust valve side rocker arms 38₁ and 38₁ in the same manner as the fixing structures of the sleeves 52₆ to 54₆ to the respective intake valve side rocker arms 33₁ to 35₁. According to the seventh modified embodiment as described above, the sleeves 52₆, 53₆, 54₆ are secured to the respective rocker arms 33₁, 34₁, 35₁ with rigidity sufficient to endure against frictional forces to be generated upon movements of switchover pins 68' and 69' by the operative-connection switchover mechanism 36₂. In this case, any distortions to be generated on the inner surfaces of the sleeves 52₆, 53₆, 54₆ are suppressed to a small value by press-fitting only the large-diameter press-fitted portions 121, 127, 133 thereby to obtain smooth movements of the switchover pins 68' and 69'. Further, since the rotors 45, 46, 47 are supported on the supporting portions 122, 128, 134 of the sleeves 52₆, 53₆, 54₆ through the rollers 55, 56, 57, which supporting portions 122, 128, 134 are only lightly press-fitted into the rocker arms whereby no distortion occurs, the rotors are supported by the rollers in a precise manner. Since the large-diameter potions 121, 133 of the sleeves 52₆, 54₆ are disposed at the side of the second intake valve side rocker arm 34₁, protruding amounts of the sleeves 52₆, 54₆ toward the second intake valve side rocker arm 34₁ at the time of press-fitting the sleeves 52₆, 54₆ can be controlled, and interference of the sleeves 52 6, 54₆ toward the second intake valve side-rocker arm 34₁ can be reliably prevented. Fig.18 illustrates an eighth modified embodiment of the sleeve fixing structure. Sleeves 52₇, 53₇, 54₇ are press-fitted into intake valve side rocker arms 33₁ to 35₁, and sleeves 59₇, 59₇ are secured to both exhaust valve side rocker arms 38₁ and 38₁ in the same manner. The sleeve 52₇ includes a large-diameter press-fitted portion 121' at its one end, a small-diameter supporting portion 122' coaxially connected to the large-diameter press-fitted portion 121' through a stepped portion 123', and an engaging portion 141 coaxially connected to the supporting portion 122' through a stepped portion 142 to be of a further smaller diameter than the supporting portion 122', and is formed into a stepped bottomed cylindrical shape closed at the other end. The first intake valve side rocker arm 33₁ is provided with, sequentially from the side of the second intake valve side rocker arm 34₁, a press-fitting hole 124' in which the large-diameter press-fitted portion 121' is press-fitted, and a small-diameter fitting hole 125' in which the engaging portion 141 is lightly press-fitted, in a coaxial manner, through the stepped portion 126' to be engaged with the stepped portion 142. A slot 143 for receiving a rotor 45₂ and rollers 55 is provided in the first intake valve side rocker arm 33₁ so as to be between the fitting hole 125' and the press-fitting hole 124. The sleeve 52₇ is secured to the first intake valve side rocker arm 33₁ by press-fitting the large-diameter press-fitted portion 121' into the press-fitting hole 124' and by lightly press-fitting the engaging portion 141 in the fitting hole 125', with the rotor 45 being supported on a supporting portion 122' of the sleeve 52₇ through a plurality of rollers 55. The sleeve 53₇ includes a large-diameter press-fitted portion 127' at one end thereof, a small-diameter supporting portion 128' coaxially connected to the large-diameter press-fitted portion 127' through a stepped portion 129', and an engaging portion 144 coaxially connected to the supporting portion 128' through a stepped portion 145 to be of a further smaller diameter than the supporting portion 128', and is formed in a stepped cylindrical shape opened at both ends. The second intake valve side rocker arm 34₁ is provided with, sequentially from the side of the third intake valve side rocker arm 35₁, a press-fitting hole 130' in which the large-diameter press-fitted portion 127' is press-fitted, and a small-diameter fitting hole 131' in which the engaging portion 144 is lightly press-fitted, in a coaxial manner, through a stepped portion 132' to be engaged with the stepped portion 145. A slot 146 for receiving a rotor 46 and rollers 56 is provided in the second intake valve side rocker arm 34₁ so as to be between the fitting hole 131' and the press-fitting hole 130'. The sleeve 53₇ is secured to the second intake valve side rocker arm 34₁ by press-fitting the large-diameter Press-fitted portion 127' in the press-fitting hole 130' and by lightly press-fit the engaging portion 144 in the fitting holes 131', and the rotor 46 is supported on the supporting portion 128' of the sleeve 53₇ through a plurality of rollers 56. The sleeve 54₇ includes a large-diameter press-fitted portion 133' at one end thereof, a small-diameter supporting portion 134' coaxially connected to the large-diameter press-fitted portion 133' through a stepped portion 135', and an engaging portion 147 coaxially connected to the supporting portion 134' through a stepped portion 148 to be of a further smaller diameter than the supporting portion 134', and is formed in a stepped bottomed cylindrical shape closed at the other end. The third intake valve side rocker arm 35₁ is provided with a press-fitting hole 136' for press-fitting the large-diameter press-fitted portion 133' into and a small-diameter fitting hole 137' for lightly press-fitting the engaging portion 147 into are coaxially provided sequentially from the side of the second intake valve side rocker arm 34₁ through a stepped portion 138' to be engaged with the stepped portion 148. A slot 149 for receiving a rotor 47 and rollers 57 is provided in the third intake valve side rocker arm 35₁ so as to be between the press-fitting hole 136' and fitting hole 137'. The sleeve 54₇ is secured to the third intake valve side rocker arm 35₁ by press-fitting the large-diameter press-fitted portion 133' into the press-fitting hole 136' and by lightly press-fitting the supporting Portion 134' in the fitting hole 137', and the rotor 47 is supported on the supporting portion 134' of the sleeve 54₇ through the plurality of rollers 57. Thus, the same effects and advantages can be provided by the eighth modified embodiment as those of the seventh modified embodiment. Fig.19 illustrates a ninth modified embodiment of the sleeve fixing structure. Serration teeth 151, 152, 153 are provided at least at one of the outer surfaces of the large-diameter press-fitted portions 121', 127', 133' at one end of sleeves 52₈, 53₈, 54₈ formed substantially in the same shape as the sleeves 52₇, 53₇, 54₇ of the eighth modified embodiment for those serration teeth to engage and be fixed to the inner surfaces of press-fitting holes 124', 130', 136' of intake valve side rocker arms 33₁, 34₁, 35₁. The sleeves 59₈, 59₈ are secured to both exhaust valve side rocker arms 38₁, 38₁ in the same manner as the fixing structure of the sleeves 52₈, 53₈, 54₈ to the intake valve side rocker arms 33₁ to 35₁ As described above, the sleeves 52₈, 53₈, 54₈ are reliably prevented from being rotated by serration engagement of the large-diameter press-fitted portions 121', 127', 133' with the rocker arms 33₁, 34₁, 35₁. Fig.20 illustrates a third embodiment of the present invention, and the same or similar reference numerals are given to components corresponding to those of the previous embodiments. A first intake valve side rocker arm 33₂ includes a first arm member 155 rockably supported on the intake valve side rocker arm shaft 37 (see Figs.2 to 4), and a second arm member 156 supported by the rocker arm shaft 37 is operatively connected to one of the intake valves adjacent to the first arm member 155 on the outside along an axial direction of the intake valve side rocker arm shaft 37. At a tip end of the first arm member 155, a bottomed cylindrical sleeve 52₉ having an axis parallel with the rocker arm shaft 37 and closed at its tip end is integrally projected toward the second arm member 156. The second arm member 156 includes a fitting hole 157 for press-fitting therein a tip end of the sleeve 52₉. The tip end of the sleeve 52₉, i.e., the closed end is lightly press-fitted in the fitting hole 157 thereby to connect the first and second arm members 155 and 156. A second intake valve side rocker arm 34₂ includes a first arm member 158 supported by the intake valve side rocker arm shaft 37 adjacent to the third intake valve side rocker arm 35₂, and a second arm member 159 supported by the rocker arm shaft 37 adjacent to the first arm member 158 at the side of the first intake valve side rocker arm 33₂. On the first arm member 158, a cylindrical sleeve 53₉ opened at both ends is integrally projected toward the second arm member 159, and a fitting hole 160 for lightly press-fitting the end of the sleeve 53₉ into is provided in the second arm member 159. The tip end of the sleeve 53₉ is lightly press-fitted into the fitting hole 160 thereby to connect the first and second arm members 158 and 159. A third intake valve side rocker arm 35₂ includes a first arm member 161 supported by the intake valve side rocker arm shaft 37, and a second arm member 162 supported by the rocker arm shaft 37 adjacent to the first arm member 161 on the outside along an axial direction of the rocker arm shaft 37. The second arm member 162 is operatively connected to the other intake valve 16. On the first arm member 161, a bottomed cylindrical sleeve 54₉ closed at the end is integrally projected toward the second arm member 162, and a fitting hole 163 for lightly press-fitting the end of the sleeve 54₉ into is provided in the second arm member 162. The tip end of the sleeve 54₉, the closed end, is lightly press-fitted in the fitting hole 163 thereby to connect the first and second arm members 161 and 162. Exhaust valve side rocker arms 38₂ and 38₂ are also constructed similar to the intake valve side rocker arms 33₂ to 35₂. In the intake valve side rocker arms 33₂, 34₂, 35₂, base ends of the first and second arm members 155, 156; 158, 159; 161, 162 are adjacently disposed so as to be interposed between both the holders 28 and 28 thereby to restrain movements of the respective arm members along an axis of the intake valve side rocker arm shaft 37. In the intake valve side rocker arms 33₂, 34₂, 35₂, the second arm member 156, 159, 162 may be formed of an aluminum alloy so as to reduce the weight, and the first arm members 155, 158, 161 that are integral with the sleeves 52₉, 53₉, 54₉ are preferably formed of metal having more rigidity than that of aluminum alloy, such as steel. According to the third embodiment, the sleeves 52₉, 53₉, 54₉ have sufficient rigidity to resist frictional forces accompanied by the movements of the switchover pins 68', 69' of the operative-connection switchover mechanism 36₂ for the intake valve side rocker arms 33₂, 34₂, 35₂. Since the sleeves 52₉ and 54₉ are only lightly press-fitted at the closed ends in the fitting holes 157 and 163, distortions are avoided at those portions for guiding the sliding of the switchover pins 68', 69' and the restrain member 70. For the second intake valve side rocker arm 34₂, the sleeve 53₉ is only lightly press-fitted in the fitting hole 160 to avoid distortion to allow the second switchover pin 69' to be slid. In this case, any distortion at the time of press-fitting can be suppressed to a small value and yet the sleeve 53₉ cannot be displaced inadvertently from the fitting hole 160 because the first and third intake valve side rocker arms 33₂, 35₂ are on both sides of the second intake valve side rocker arm 34₂. Further, the rocker arms 33₂, 34₂, 35₂ can be assembled in advance by lightly press-fitting the sleeves 52₉, 53₉, 54₉ into the fitting holes 157, 160, 163 for ease in assembling them to the intake valve side rocker arm shaft 37, thereby improving the assembling process. It should be noted that for the first and third intake valve side rocker arms 33₂, 35₂ the sleeves 52₉, 54₉ may be provided on either of the first and second arm members 155, 156; 161, 162. Fig.21 illustrates a fourth embodiment of the invention, and the same or similar reference numerals are given to components corresponding to those of the previous embodiments. A high speed cam 29' for the intake valves to be provided on the cam shaft 26 includes a base circle portion 29'a having a smaller diameter than those of base circle portions 30a, 31a of the intermediate speed cam 30 and the low speed cam 31 for the intake valves provided on the cam shaft 26 at opposite sides of the cam 29', and a lobe 29'b extended radially outward from the base circle portion 29'a. Secured to a first intake valve side rocker arm 33₁ is a cylindrical sleeve 52₁₀ for rotatably supporting a cylindrical rotor 45 in rolling contact with the intermediate speed cam 30 for the intake valves. Secured to a second intake valve side rocker arm 34₁ is a cylindrical sleeve 53₁₀ for rotatably supporting a rotor 46' in rolling contact with the high speed cam 29' for the intake valve. Secured to a third intake valve side rocker arm 35₁ is a cylindrical sleeve 54₁₀ for rotatably supporting a rotor 47 in rolling contact with the low speed cam 31 for the intake valves. In addition, the outer diameter D₁ of the rotor 46' in rolling contact with the high speed cam 29' for the intake valves is larger than the outer diameters D₂ of the other rotors 45, 47. The sleeves 52₁₀, 53₁₀, 54₁₀ have the same inner diameter. However, the outer diameter of the sleeve 53₁₀ is formed larger than those of the sleeves 52₁₀ and 54₁₀. In the first intake valve side rocker arm 33₁, a bottomed fitting hole 49 opened on the side of the second intake valve side rocker arm 34₁ is provided in parallel with the intake valve side rocker arm shaft 37. In the second intake valve side rocker arm 34₁, a small-diameter fitting hole 50a is provided at the side of the first intake valve side rocker arm 33₁ and a large-diameter fitting hole 50b forming a stepped portion 50c between the hole 50b itself and the small-diameter fitting hole 50a is coaxially provided. In the third intake valve side rocker arm 35₁, a bottomed fitting hole 51 opened on the side of the second intake valve side rocker arm 34₁ is provided in parallel with the intake valve side rocker arm shaft 37. Further, the fitting hole 49 is provided with a recess 49a recessed axially inward at an end thereof near the second intake valve side rocker arm 34₁, the hole 50b is provided with a recess 50d recessed axially inward at an end thereof near the third intake valve side rocker arm 35₁, and the hole 51 is provided with a recess 51a recessed axially inward at an end thereof near the second intake valve side rocker arm 34₁. A locking stepped portion 171 facing the side of the second intake valve side rocker arm 34₁ is annularly provided at the outer face of the sleeve 52₁₀ on the side of the second intake valve side rocker arm 34₁. The sleeve 53₁₀ is provided at its one end with a small-diameter portion 172 fitted in the small-diameter fitting hole 50a, and is fitted in the large-diameter fitting hole 50b. A locking stepped portion 173 facing the side of the third intake valve side rocker arm 35₁ is annularly provided at the outer face of the other end of the sleeve 53₁₀. Further, a locking stepped portion 174 facing the side of the second intake valve side rocker arm 34₁ is annularly provided on the sleeve 54₁₀ on the outer face of the side of the second intake valve side rocker arm 34₁, which sleeve 54₁₀ is mounted in the fitting hole 51. The sleeve 52₁₀ is secured to the first intake valve side- rocker arm 33₁ by caulking the inner peripheral surface of the recess 49a at the locking stepped portion 171 with the sleeve fitted in the fitting hole 49. The sleeve 53₁₀ is secured at the large-diameter portion 172 to the second intake valve side rocker arm 34₁ by caulking the inner peripheral surface of the recess 50d at the locking stepped portion 173. The sleeve 54₁₀ is secured to the third intake valve side rocker arm 35₁ by caulking the inner peripheral surface of the recess 51a at the locking stepped portion 174. A plurality of rollers 55, 56' 57 are interposed between the sleeves 52₁₀ to 54₁₀ and rotors 45, 46', 47 which coaxially surround the sleeves 52₁₀ to 54₁₀. According to the fourth embodiment, the high speed cam 29' is the cam having the largest lift amount for the intake valves 16 among the high speed cam 29', the intermediate speed cam 30, and the low speed cam 31 provided on the cam shaft 26 corresponding to the intake valve side rocker arms 33₁, 34₁, 35₁. The outer diameter D₁ of the rotor 46' in rolling contact with the high speed cam 29' is larger than the outer diameters D₂ of the other rotors 45, 47. Accordingly, the peripheral speed of the contact surface of the large-diameter rotor 46' with the high speed cam 29' caused by the rotation of the cam shaft 26 is faster than those of the contact surfaces of the small-diameter rotors 45, 47 with the cams 30, 31. Thus, wearing amounts of the contact surface of the rotor 46' with the high speed cam 29' and of the contact surfaces of the rotors 45, 47 with the cam 30, 31 can be substantially equalized, the displacements of the axes of the sleeves 52₁₀, 53₁₀, 54₁₀ are prevented even in the case of operation for a long period, and the switching operation of the operative-connection switchover mechanism 36₂ can be smoothly maintained. In addition, the outer diameters of the rotors 45, 47 are not increased more than necessary, and the weights are not increased more than required either. Therefore, this construction can contribute to a reduction in the valve operating load. Further, more rollers 56' can be interposed between the sleeve 53₁₀ and the rotor 46' by increasing the outer diameter of the sleeve 53₁₀ larger than the outer diameters of the sleeves 52₁₀, 54₁₀, and sufficient durability for the relatively large load can be incorporated in the rollers 56'. Fig.22 illustrates a tenth modified embodiment of the sleeve fixing structure. A cylindrical sleeve 52₁₁ for rotatably supporting rotor 45 is secured to a first intake valve side rocker arm 33₁. A cylindrical sleeve 53₁₁ for rotatably supporting a rotor 46' is fixedly secured to a second intake valve side rocker arm 34₁. A cylindrical sleeve 54₁₁ for rotatably supporting a rotor 47 is secured to a third intake valve side rocker arm 35₁. The sleeve 52₁₁ is fitted in a bottomed fitting hole 49 provided in the first intake valve side rocker arm 33₁. The sleeve 53₁₁ is engaged with a fitting hole 50 provided in the second intake valve side rocker arm 34₁. The sleeve 54₁₁ is engaged with a fitting hole 51 provided in the third intake valve side rocker arm 35₁. A C-shaped snap ring 175 mounted on the outer surface of the sleeve 52₁₁ is engaged with an annular locking groove 176 in the inner surface of the fitting hole 49 thereby to restrain the axial movements of the sleeve 52₁₁. A C-shaped snap ring 177 mounted on the outer surface of the sleeve 53₁₁ is engaged with an annular locking groove 178 in the inner surface of the fitting hole 50 thereby to restrain the axial movements of the sleeve 53₁₁. A C-shaped snap ring 179 mounted on the outer surface of the sleeve 54₁₁ is engaged with an annular locking groove 180 in the inner surface of the fitting hole 51 thereby to restrain the axial movements of the sleeve 54₁₁. Fig.23 illustrates an eleventh modified embodiment of the sleeve fixing structure. A cylindrical sleeve 52₁₀ for rotatably supporting a rotor 45 is fitted in a fitting hole 49 of a first intake valve side rocker arm 33₁. A ring-like locking member 181 is engaged with a locking stepped portion 171 of the sleeve 52₁₀. The locking member 181 is fitted into and caulked with the annular locking groove 176 of the fitting hole 49 thereby to secure the sleeve 52₁₀ to the first intake valve side rocker arm 33₁. Further, the cylindrical sleeve 53₁₀ is fitted in the small-diameter fitting hole 50a and the large-diameter fitting hole 50b of the second intake valve side rocker arm 34₁. A ring-like locking member 182 is engaged with the locking stepped portion 173 of the sleeve 53₁₀. The locking member 182 is fitted into and caulked with the annular locking groove 178 of the small-diameter fitting hole 50a thereby to secure the sleeve 53₁₀ to the second intake valve side rocker arm 34₁. In addition, the sleeve 54₁₀ is fitted in the fitting hole 51 of the third intake valve side rocker arm 35₁. A ring-like locking member 183 is engaged with the locking stepped portion 174 of the sleeve 54₁. The locking member 183 is fitted into and caulked with the annular locking groove 180 of the fitting hole 51 thereby to secure the sleeve 54₁₀ to the third intake valve side rocker arm 35₁. Figs.24, 25 and 26 illustrate a twelfth modified embodiment of the sleeve fixing structure. Fig.24 is a cross-sectional view, Fig.25 is a perspective view of a sleeve to be fixed to a third intake valve side rocker arm, and Fig.26 is a perspective view of a sleeve to be fixed to a second intake valve side rocker arm. A sleeve 52₁₂ is secured to a first intake valve side rocker arm 33₁. A sleeve 53₁₂ is secured to a second intake valve side rocker arm 34₁. A sleeve 54₁₂ is secured to a third intake valve side rocker arm 35₁, As shown in Fig.25, the sleeve 54₁₂ is formed in a cylindrical shape having a locking stepped portion 174 disposed at an end on the side of the second intake valve side rocker arm 34₁. A fitting protrusion 185 protruding axially outward is provided at the other end of the sleeve 54₁₂. A bottomed fitting hole 51 in which the sleeve 54₁₂ is fitted is provided in the third intake valve side rocker arm 35₁. A fitting recess 186 in which the fitting protrusion 185 is fitted is provided at the closed end of the fitting hole 51. The fitting recess 186 may be a through hole as shown in Fig.24 or a bottomed hole. The ring-like locking member 183 is connected to the locking stepped portion 174 of the sleeve 54₁₂ fitted in the fitting hole 51 by fitting the fitting protrusion 185 into the fitting recess 186. The locking member 183 is fitted into and caulked with the annular locking groove 180 thereby to secure the sleeve 54₁₂ to the third intake valve see-rocker arm 35₁in a state where the sleeve 54₁₂ is prevented from being rotated around its axis. As shown in Fig.26, the sleeve 53₁₂ is formed in a cylindrical shape and is provided at its one end with a locking stepped portion 173 facing the side of the third intake valve side rocker arm 35₁ and at the other end with a small-diameter portion 172 to be fitted in the small-diameter fitting hole 50a of the second intake valve side rocker arm 34₁. A connecting protrusion 187 protruding radially outward from the outer surface of the small-diameter portion 172 is provided at the other end of the sleeve 54₁₂. A connecting recess 188 to which the connecting protrusion 187 is engaged is provided on the inner surface of the small-diameter fitting hole 50a provided in the second intake valve side rocker arm 34₁. The ring-like locking member 182 is engaged with the locking stepped portion 173 of the sleeve 53₁₂ with the sleeve 53₁₂ fitted in the small-diameter fitting hole 50a and the large-diameter fitting hole 50b such that the connecting protrusion 187 is engaged with the connecting recess 188. The locking member 182 is fitted into and caulked with the annular locking groove 178 thereby to secure the sleeve 53₁₂ to the second intake valve side rocker arm 34₁ in a state where the sleeve 53₁₂ is prevented from being rotated around its axis. The sleeve 52₁₂ is formed into a cylindrical shape having at its one end the locking stepped portion 171 facing the side of the second intake valve side rocker arm 34₁. The sleeve 52₁₂ is also provided at its outer end with a fitting protrusion 189 protruding axially outward similar to protrusion 185. The bottomed fitting hole 49 in which the sleeve 52₁₂ is fitted is provided in the first intake valve side rocker arm 33₁. A fitting recess 190 in which the fitting protrusion 189 is fitted is provided at the closed end of the fitting hole 49. The fitting recess 190 may be a through hole as shown in Fig.24 or a bottomed hole. The ring-like locking member 181 is engaged with the locking stepped portion 171 of the sleeve 52₁₂ fitted in the fitting hole 49 such that the fitting protrusion 189 is fitted in the fitting recess 190. The locking member 181 is fitted into and caulked with the annular locking groove 176 thereby to secure the sleeve 52₁₂ to the first intake valve side rocker arm 33₁ in a state where the sleeve 52₁₂ is prevented from being be rotated around its axis. Figs.27, 28 and 29 illustrate a thirteenth modified embodiment of the sleeve fixing structure. Fig.27 is a cross-sectional view, Fig.28 is a view taken along line 28-28 of Fig.27, and Fig.29 is a front view of a locking member. A sleeve 52₁₃ is secured to a first intake valve side rocker arm 33₁. A sleeve 53₁₃ is secured to a second intake valve side rocker arm 34₁. A sleeve 54₁₃ is secured to a third intake valve side rocker arm 35₁. A plurality of, for example three, locking grooves 191 are formed at intervals in a circumferential direction on the outer surface of one end of the sleeve 54₁₃. A plurality of recesses 51a facing axially inward is provided at the open end of the bottomed fitting hole 51 provided in the third intake valve side rocker arm 35₁ such that the sleeve 54₁₃ is fitted in the open end. Locking collars 192 extending radially inward are provided at a plurality of positions, for example, three positions at intervals in a circumferential direction of the open end of the recess 51a. A ring-like locking member 193 having a sufficient inner diameter so that the sleeve 54₁₃ can fit therein is contained in the recess 51a of the third intake valve side rocker arm 35₁. Engaging protrusions 194 are projected so as to be disposed between the locking collars 193 around the outer periphery of the locking member 192 when the locking member 193 is contained in the recess 51a. Engaging pawls 195 are provided around the inner periphery of the locking member 193 corresponding to the locking grooves 191 provided on the sleeve 54₁₃. The engaging protrusions 194 of the locking member 193 are caulked to the locking collars 192 in a state where the locking member 193 is contained in the recess 51a of the third intake valve side rocker arm 35₁ with the sleeve 54₁₃ being fitted in the fitting hole 51. The connecting pawls 195 are caulked to the locking grooves 191 of the sleeve 54₁₃ thereby to secure the sleeve 54₁₃ to the third intake valve side rocker arm 35₁. The sleeve 54₁₃ is secured to the second intake valve side rocker arm 34₁ by using a locking member 196 similar to locking member 193 of the fixing structure for the sleeve 54₁₃ to the third intake valve side rocker arm 35₁. Similarly, the sleeve 52₁₃ is secured to the first intake valve side rocker arm 33₁ by using a locking member 197.

Claims: An SOHC-type valve operating system in an internal combustion engine having a single cam shaft (26) commonly provided for a pair of intake valves (16) and a pair of exhaust valves (20), a plurality of intake valve driving members (33₁-35₁, etc.) rockably disposed between said cam shaft (26) and said pair of intake valves (16) and having an operative-connection switchover mechanism (36₁; 36₂) for switching-over between an operative connection and disconnection of the intake valve driving members (33₁-35₁, etc.) and a pair of exhaust valve driving members (38₁, 38₁, etc.) rockably disposed between said cam shaft (26) and said pair of exhaust valves (20) and respectively corresponding to said exhaust valves, wherein said operative-connection switchover mechanism (36₁; 36₂) comprises switchover pin means (68-70, etc.) movable between a position for operatively connecting adjacent intake valve driving members and a position for releasing such connection, and a plug pipe (79) is provided in a cylinder head (9) in which pipe an ignition plug (78) is to be inserted, characterized in that cylindrical sleeve means (52₁-54₁, etc.) is secured to said intake valve driving members (33₁-35₁, etc.) for guiding the movement of said switchover pin means (68-70, etc.), that said cylindrical sleeve means (52₁-54₁, etc.) rotatably supports a cylindrical rotor (45-47, etc.) thereon which is in rolling contact with a cam (29-31) provided on said cam shaft (26), that said operative-connection switchover mechanism (36₁; 36₂) is disposed at an opposite side of said intake valves (16) with respect to a rocking axis of said intake valve driving members (33₁-35₁, etc.), and that said plug pipe (79) is provided between said pair of intake valves (16). An SOHC-type valve operating system in an internal combustion engine according to claim 1, wherein at least one of said plurality of intake valve driving members (34₁, etc.) is free from connection to said intake valves (16) when said operative-connection switchover mechanism (36₁; 36₂) is in a state releasing the operative connection, and a lost motion mechanism (62) for resiliently urging said at least one intake valve driving member (34₁, etc.) toward said cam (29) is disposed above and engages said at least one intake valve driving member. An SOHC-type valve operating system in an internal combustion engine according to claim 1, wherein said engine is a V-type internal combustion engine having an intake port (10) inside of each bank. An SOHC-type valve operating system in an internal combustion engine according to claim 1, wherein at least one of said intake valve driving means (33₁, etc.) has a cylindrical hole (125, etc.) extending parallel to said rocking axis for receiving said cylindrical sleeve means (52₆, etc.), said cylindrical sleeve means (52₆, etc.) has an outer cylindrical surface with at least two portions with different diameters, one (121, etc.) of said portions of the outer cylindrical surface having a largest diameter being press-fitted into a portion (124, etc.) of said cylindrical hole for securing said cylindrical sleeve means (52₆, etc.) to said one intake valve driving means (33₁, etc.). An SOHC-type valve operating system in an internal combustion engine according to claim 1, wherein said cylindrical sleeve means (52₁₀, etc.) and said intake valve driving members (33₁, etc.) to which the cylindrical sleeve means is secured have adjacent axially countersunk portions (171, etc.) at locations on at least one axial end of said cylindrical sleeve means (52₁₀, etc.) and securing means (181, etc.) is located in said countersunk portions (171, etc.) for securing said cylindrical sleeve means (52₁₀, etc.) to said associated intake valve driving members (33₁, etc.), said securing means being comprised of a locking member (181, etc.) fitted in a groove (176, etc.) provided in one or both of said cylindrical sleeve means and associated intake valve driving member, said locking member (181, etc.) engaging both said cylindrical sleeve means (52₁₀, etc.) and associated intake valve driving member (33₁, etc.) and wherein said system further includes means for permanently securing said locking member (181, etc.) to one or both of said cylindrical sleeve means and associated intake valve driving member.

Inventors: ARAI HIDEMI C O K K HONDA, FUJIYOSHI YOSHIHIRO C O K K HO, FUKUO KOICHI C O K K HONDA, FUKUZAWA MASAMI C O K K HONDA, KOBAYASHI MASAYUKI C O K K HON, NISHIDA SHINICHI C O K K HONDA, SHIMOYAMA KAZUAKI C O K K HOND, SUGAI TAKASHI C O K K HONDA, SUGIMOTO CHIHAYA C O K K HONDA, ARAI, HIDEMI, C/O K.K. HONDA, FUJIYOSHI, YOSHIHIRO, C/O K.K. HONDA, FUKUO, KOICHI, C/O K.K. HONDA, FUKUZAWA, MASAMI, C/O K.K. HONDA, KOBAYASHI, MASAYUKI, C/O K.K. HONDA, NISHIDA, SHINICHI, C/O K.K. HONDA, SHIMOYAMA, KAZUAKI, C/O K.K. HONDA, SUGAI, TAKASHI, C/O K.K. HONDA, SUGIMOTO, CHIHAYA, C/O K.K. HONDA
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1994
Main classification: F01L1
IPC codes: F01L1, F02F1, F01L13